1. Field of the Invention
The field of the invention relates generally to solid state motor actuators. More particularly, the invention relates to a piezoelectric solid state motor with a solderless connector for connecting electrodes to a power source.
2. Related Art
For decades electroexpansive materials have been employed in stacked structures for producing actuation used for fuel injection and valve control in diesel engines, for example. Commercially manufactured solid state motor stacks, or actuators, are produced using piezoelectric disks interleaved with metal foil electrodes. Application of high voltage (e.g., 1000 v dc), low current power to alternately biased electrodes causes each of the piezoelectric disks to expand or axially distort. The additive deflection of the stacked disks is typically amplified by hydraulics to effectuate useful actuation.
An example of a conventional electromechanical actuator having an active element of electroexpansive material is found in U.S. Pat. No. 3,501,099 to Glendon M. Benson (the '099 patent). The '099 patent is directed to both an actuation amplification structure and a method for manufacturing piezoelectric stacks.
The method for manufacturing piezoelectric stacks is essentially comprised of the following steps. Sheets of ceramic material are rolled, compacted and punched into ceramic disks. After a cleaning process, the disks are stacked with alternate sets of continuous disk electrodes disposed between the ceramic disks.
Alternate electrodes of each disk/electrode structure (stack) are interconnected to one another using straps, thereby forming a first electrode group. A second electrode group is similarly interconnected. Each electrode group is called a "chain electrode".
The stacks then undergo a pressurized cool-welding process, followed by an elevated temperature and pressure bonding process after lead wire electrodes are connected to the two chain electrodes. The stacks are poled by application of a dc voltage, and are then encapsulated with a plastic insulative cover prior to final mounting within a transducer housing.
The '099 patent's electrode structure represents a common serial approach to electrode interconnection. Another common interconnection scheme is the bus bar approach.
The bus bar scheme uses a common bar or wire to connect every other electrode in a parallel fashion. Each electrode includes a tab portion extending tangentially from a point on the circumference of the electrode. The tabs facilitate soldering or welding of the bus bar to the electrodes. Conventionally, each stack uses two bus bars to connect the power supply leads to the two respective electrode groups.
Both of the above discussed electrode interconnection structures suffer from various disadvantages. The chain electrode structure makes assembly of ceramic disk/electrode stacks difficult, and the foil conventionally used for the chain electrode is fragile. In contrast, structurally, the bus bar becomes somewhat ridge due to the soldering of the many tabs, thus, inhibiting stack actuation. Further, assembly and soldering of the bus bar structure requires many process steps.
The present invention overcomes the deficiencies of the conventional technology noted above.